If started advertising and you have selected the keywords you wish to promote, you could anticipate that when you type in one of these terms into the search engine, one of your advertisements will show up. However, this is not always the case. Search engines can be quite complex - below are the top 3 reasons why you may not be seeing your ads:
You keep looking to ads for keyword 'X' but you don't click on an ad.
If you keep repeatedly searching for keywords that match yours, without actually clicking on the ads that are shown to you (remember, it will cost you money!), then Google/Microsoft may choose to show you different ads in the future. This is ironic, as the more you look for your own ad, the less likely you are to see it!
Your budget is too low
If a keyword you’re targeting is very popular, but you have limited funds, Google/Microsoft may not always display your advertisement. For instance, if the phrase is searched 20,000 times per day and you’ve got a 2% clickthrough rate, this would equate to 400 clicks. If each click cost you 50 cent, your daily expenditure would be €200. Since your budget could be as little as €10, your ad may only be visible 5% of the time.
You may not be located in the targeted region or looking during the targeted time of day.
If you are targeting your advertisements to certain geographical areas and/or certain times of day, make sure to check that you are in the selected area and search during the designated times. Even if you are not intentionally targeting a specific location or time, Google's/Microsoft's machine learning-based bidding strategies will likely display your ads more often and higher if they think you are more likely to purchase the product or service. If Google doesn't think you are likely to make the purchase, your advertisement may not be shown whatsoever.